(a) Field of the Invention
The present invention relates to a girder block lifting method and a jack-up stage used therefor and especially relates to a girder block lifting method which is preferable when a boiler module for a thermal power plant is lifted by a girder of a steel frame for an installation work and a jack-up stage used therefor.
(b) Description of the Related Art
In a thermal power plant having a large-scale pendant boiler, steel beams of a building are set and on top edge portions of the steel beam, a girder for supporting the boiler is provided to bridge the top edge portions and to support boiler component parts by hanging. For this configuration, a lifting construction method is generally used. In this method, modules of the boiler component parts carried in the steel frame are lifted up to the girder from the ground for several tens of meters by use of a plurality of lifting jacks provided on the girder and then the modules are hung and supported from the girder by use of a sling rod or the like. Such an operation is repeatedly carried out from the module assembled on the upper part of the boiler to the module assembled on the lower part of the boiler successively to construct a boiler equipment.
To the boiler module, collateral machineries are assembled in the middle of the operation on the ground or lifting operation. However, to avoid operation in a high spot, the machineries are assembled in a condition where the module is supported by a temporary beam provided on the ground side or is hung by the lifting jack in many cases. Moreover, there is known a method to avoid hanging heavy materials at a position high from ground. According to this method, as shown in FIG. 8, girder joint portions 2 are formed in a projecting manner inside upper edge portions of a pair of beams among a plurality of provided steel beams 1 and a lifting jack 3 is installed on the upper surfaces of the girder joint portions 2. Then, a girder 4 is hung by a lifting sling 5 of the lifting jack 3 on the ground and machinery 6 to be hung from the grinder 4 is assembled by operation on the ground while the girder 4 is gradually jacked up. Such operations are repeated and when the girder 4 is finally connected to the girder joint portions 2 and fixed to the top of the steel beam 1, many of the lower boiler modules are assembled. Thus, it becomes possible to significantly reduce the amount of operation at high places. Similar construction method can be seen in the Patent Document 1. According to the document, a boiler block is hung from a girder while assembly is proceeded and finally, the girder is jacked up to a steel beam to be moved to the top edge portion of the steel beam for installation. As related inventions, techniques described in the Patent Documents 2 and 3 are also known.    [Patent Document 1] Japanese Unexamined Patent Publication No. H11-100902    [Patent Document 2] Japanese Unexamined Patent Publication No. H11-081684    [Patent Document 3] Japanese Unexamined Patent Publication No. H08-114302
However, according to the conventional construction method of hanging the module with the girder, the girder 4 is temporarily placed on the ground and is gradually hung up for several tens of meters by a lifting jack installed at the girder joint portions on the top edge portions of the steel beams while the boiler modules are assembled. Therefore, there is a problem that the steel beams would incline or collapse inward due to lifting of heavy materials. Therefore, to prevent inclination or collapse of the steel beams 1, truss-structured large frames 7 and 8 are generally constructed as projecting toward the back surface side of the steel beam in a jetty manner as shown in FIG. 8. Otherwise, as described in the Patent Document 1, a method has been adopted by which amount of inclination of the steel beam is acquired from the moment applied to the steel beam and the steel beam is inclined in the reverse direction in advance for the expected degree of inclination while the steel beam is retained by a frame so that the inclination is balanced out. Therefore, in the conventional construction method, construction equipment becomes large due to the large frames 7 and 8 for supporting the steel beam and there occurs a problem that the construction cost becomes high.
Moreover, according to the conventional method, the girder must be lifted between a pair of steel beams and joint fixed on the upper edge portions of the steel beams 1 and therefore the girder joint portions 2 are formed in a projecting manner on the inner surfaces of the upper edge portions of the steel beams 1, where the lifting jack 3 is mounted, and a lifting rod is connected to the girder for lifting. Therefore, shape of the girder joint portions 2 must be a special shape such as crossly-cut one so that a lifting rod hung from the lifting jack mounted on the upper surface of the girder joint portion 2 can be connected to the girder. Further, if the girder joint portion is shaped to have a special shape, there is a problem that the steel beam cannot be used for other construction methods using a girder which has a standard specification of other company.